**Despite the promo on the cover about “Nobel Prize in Physics 2017”, I think sales of “GRAVITATION” have ebbed since last year. Why? It doesn’t fit into any course curriculum. It’s a THICK book, weighing in at 25 lb. Written as two versions in one: Track 1 for most folks with a background in simple partials; Track 2 for the top 5% who can appreciate the mathematical rigor of tensor mathematics.**

At the end of the last discussion panel in an amazing initial conference of the ‘OSI’ held in the East Sage restaurant of UBC (the old Faculty Club) and bringing serious people together from all realms on the topics of – to quote the flyer – “Space Colonization” (sic), “Space Mining”, “Space Debris”, and “Canadian Space Policy” one Associate Professor from Texas expressed some intense angst,

**“I wish I could teach my students, gravitation. I mean to say, I wish they didn’t constantly hear about how space travel is weightless – no gravity on the International Space Station. There is gravity everywhere!”**

Yes, there is. Gravity IS “everywhere”… and every “when.”

You see, Gravity IS Spacetime. That is the message of the book * GRAVITATION* in its simplest, rudimentary form. Not all of the book. Certainly not all of Track 2, but that’s it. The math to get to that statement definitively, makes its simpler. The math is not simple, but it makes it crystal clear.

However, our educational system makes it nearly impossible for my friend from Texas to teach gravity the way it is, and needs to be taught. My student, who teaches Physics in Seattle told me how it is now. First he must teach Newtonian physics, then the students prepare for the examination. Then, they learn Quantum Physics, and they prepare for those tests. Ad nauseum. “It’s a curriculum, stupid.” He didn’t say I was stupid. He never would, but like all dedicated instructors he was “sharing the angst.”

My simple-minded approach is to begin by stating, “We live in a 4-dimensional universe as far as we can determine. Not space here and time there, but like **Tacocat**, the musical group from Seattle. Three women (like 3 space coordinates) and one guy (a dimension of time). **Not tacos here and cats there**. Like **Tacocat,** the *palindrome* (thanks Molly!). **Tacocat** is like gravity. Like spacetime.”

**SPACETIME PHYSICS PART 1**

“Wherein the reader is led, once quickly, then again more slowly, down the highways and a few byways of Einstein’s geometrodynamics – without the benefit of a good mathematical compass.”

Gravity is not a force. It acts on nothing. Here or ‘at a distance’. It is spacetime. All material objects travel unimpeded in spacetime. They travel in straight lines in spacetime. We give these straight lines special names, “World Lines”, to distinguish them from ordinary Cartesian lines or vectors in space.

Elliptical orbits, like the Earth around the Sun, are illusory for us. They are not illusions, however. As any Wall Street broker knows, before he takes “the plunge,” gravity is no illusion. In spacetime, the Earth travels in a straight line around the Sun.

Wait! How is that possible? To travel in a straight line *around* anything?

The only way to ‘imagine’ this first lesson – without math we can only imagine – is to look locally at Newton’s apple on the book’s cover, above. It is a three-dimensional apple. If an ant tries to walks a two dimensional course around the stem, for example, never overtly varying locally from point-to-point on its straight line course, it will circle the stem.

It will seem to the ant this encircling is cause by an unknown “force”. Perhaps caused by the stem itself, which causes it to move around the stem and veer from its straight line course. It “feels” a pull, perhaps toward the stem. That is the reason, then. It moves in a circular course around the stem, because of a “* central stemforce*.”

The same is true if it walked a two-dimensional course around the ‘equator’ of the apple, further from the apple’s stem. Locally, it tries to walks from point-to-point in a straight line which it verifies in two-dimensions, but it will circle the stem and meet its own tracks, perhaps. It will “feel” the “* central stemforce*.” But it is a “weaker” force further from the stem. It takes longer and is a longer path to circle the stem. Of course, the

*is imaginary.*

**central stemforce**Like gravity, in our Universe IS spacetime. And from Einstein’s point of view, every material object gets its ‘marching orders’ locally from spacetime. Locally, the ant moves in a flat two-dimensional world as we move, locally, in a three-dimensional world. From Einstein’s point of view, the lines meet in the far, global spacetime.

Of course, we are trying to pull you into the world of Geometrodynamics or the greatest ambitions of Einstein’s General Relativity, where *acceleration* and *gravity* are indistinguishable. A well-contented student might believe they understand General Relativity. But this analogy has its limits and illusory qualities. Buy the book – * GRAVITATION* and teach it. This is your only saving grace.